1. Field of the Invention
The present invention relates to a crystalline form of (3R,4R)-4-[3-(S)-hydroxy-3-(6-methoxyquinolin-4-yl)propyl]-1-[2-(2-thienylthio)ethyl]piperidine-3-carboxylic acid, represented by the structure: 
2. Description of the Art
(3R,4R)-4-[3-Hydroxy-3-(6-methoxyquinolin-4-yl)propyl]-1-[2-(2-thienylthio)-ethyl]piperidine-3-carboxylic acid and its preparation has been disclosed in U.S. Pat. No. 6,403,610, the disclosure of which is hereby incorporated by reference, in the form of 2 diastereoisomers, known as diastereoisomer A and diastereoisomer B. In U.S. Pat. No. 6,403,610, the diastereoisomers obtained existed in the amorphous form. Among the diastereoisomers of this quinolylpropylpiperidine derivative, diastereoisomer A, (3R,4R)-4-[3-(S)-hydroxy-3-(6-methoxyquinolin-4-yl)propyl]-1-[2-(2-thienylthio)ethyl]piperidine-3-carboxylic acid, is particularly advantageous for its antibacterial activity, in particular with regard to microorganisms such as Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecium or Moraxella catharrhalis. It is also highly advantageous because of its good activity, both by the oral route and by the injectable route, and because of its low toxicity.